The present invention relates to a device in which a hydraulic retarder used for large scale vehicles such as buses, trucks, etc. and a parking brake are united, and the performance of the fluid type retarder is improved.
Usually, there are three kinds of braking devices for motor cars, depending on the purposes for use: routine brake, parking brake and reduction device. Among them, the routine brake is a treadle type brake which brakes all of the wheels and is used for deceleration and stopping of the vehicle. The parking brake is a manual brake and there are both a type to act on the same elements as the routine brake for rear wheels, but through a different transmission mechanism, and a center brake used exclusively for parking by attaching to the transmission or the propeller shaft. The parking brake can be used for assistance at a time of breakdown of the routine brake and for stopping the vehicle at the time of emergency.
As such a parking brake, a duo-servo type drum brake is used generally, in which two brake shoes each laminated with brake lining on a semicircular member are connected through a link inside a brake drum rotatable with a wheel axle, and the rotation of the wheel axle is stopped by pressing these shoes against the brake drum through the operation of a parking lever.
The deceleration device is used for large scale trucks or buses due to the danger that, when descending a long slope, the braking performance is lowered with the routine brake alone due to the heat generation at the friction portion of the brake, and there must exist an exhaustion brake, hydraulic retarder, electromagnetic retarder, etc. Among them, the hydraulic retarder (hereinafter simply referred to as a retarder) exhibits a preferable characteristic as the deceleration device in that the absorbed horse power increases abruptly with an increase in the number of revolutions and is assembled most frequently into the transmission or the driving device of the rear wheels.
As shown in FIG. 3, the body of the retarder aforementioned is fixed radially with the wheel axle (101) as a center. A vane chamber (104) is provided around the wheel axle (101) and contains a plurality of rotor vanes (102) which rotate with the wheel axle (101) and is surrounded by a vane chamber case (103) stator vanes (105) fixed to the vane chamber case (103) are formed in said vane chamber (104) oppositely to the rotor vanes (102). For operating the retarder, cooling oil (A) is supplied to a portion between the opposing rotor vanes (102) and the stator vanes (105) in the vane chamber (104) to transmit the energy of rotating rotor vanes (102) to the circulating cooling oil as heat due to the viscosity of the cooling oil resulting in the deceleration.
Numeral (106) is a tank of cooling oil and numeral (107) shows an oil pump feeding the cooling oil to the retarder.
The control of the working of this retarder is accomplished by means of controlling the flow rate of cooling oil to be supplied into the vane chamber, that is, the level of the oil surface. Therefore, retardation is eliminated by discharging the cooling oil. However, retardation of retarder due to the remaining cooling oil that is, the drag torque, remains. Further, there have been such problems that the device for controlling the level of the oil surface is expensive and heavy in weight.
Moreover, the uniting of the retarder with the parking brake has been desired strongly for compactness and light weight.
The purpose of the invention is to provide a fluid type retarder attached with a parking brake, which eliminates the generation of said drag torque and is capable of being manufactured at low cost.